The invention relates to the indication of the level of a liquid in a container by the use of a total-reflection refractive optical device, whose properties of transmitting a light ray are modified when the surface of reflection is wetted by the liquid.
The detection of one or more fixed levels using one or more fixed prisms or cones combined with fibre optics, is known, in particular according to French Pat. No. 2,213,487. Such a device provides information only at the instant when a given level is reached but gives no exact indication of the level in other circumstances.
A device with an optical prism integrated with the light transmitter and receiver and which allows remote operation by means of electrical wires rather than fibre optics, is also known, from British Pat. No. 888,941. However, here again the prisms are always in a fixed position, with the same drawbacks as above.
Also a level indicator device which, in one particular form, makes use of prisms which are able to move vertically by means of a screw, but in which the light transmitter and receiver are always fixed with remote transmission of the light, is also known, in particular according to French Pat. No. 1,593,760. The optical, electronic and mechanical assembly is then complex and delicate.